When you add the Execute Macro action, one of the options in the drop-down menu is This Macro Group:
When you add the Execute a Subroutine action, that option isn't included:
It would be oh-so-nice if the Execute Subroutine action had that same This Macro Group option. I use subroutines in most of the macros I distribute, and many are identically named because they do the same thing. Hence it's a real pain to make sure I find the right subroutine in the long list.
The This Macro Group option makes it extremely simple to select the right macro, and it would be just as useful in selecting the right subroutine.